MI-1. The first production helicopter in the USSR.
Is it really interesting? How this amazing (without exaggeration) aircraft not only stays in the air, but also flies beautifully. How beautiful it is! I have repeatedly witnessed serial aerobatics combat helicopter MI-24 over the airfield of the city of Brzeg in Poland. The helicopter is already an honored veteran, but it is a formidable combat vehicle that has proven itself well in Afghanistan, and it flies in such a way that it takes your breath away, and it is impossible to take your eyes off this action.
So what allows her to do this? After all, it seems like an awkward aircraft compared to an airplane. At the risk of repeating myself once again, I will say that in fact the principle of helicopter flight is quite simple. And we already know something to explain it.
Have you probably heard the common expression “rotorcraft”? It's quite correct. An airplane is held in the air by a wing, while in a helicopter these functions are performed by a large diameter propeller. It is called the main rotor. Each blade main rotor is, in fact, a wing that has an aerodynamic profile and moves when the propeller rotates in the air flow. That's probably all that matters :-). We have already figured out what happens to the wing. There is an aerodynamic force applied to each blade and, as their sum, a total force applied to the propeller and through it to the entire helicopter. This force is always perpendicular to the plane of rotation of the screw.
Forces acting on a helicopter.
If it is directed upward and is greater than the weight of the helicopter, then it rises vertically; if it is equal to the weight, then it hangs in the air. Simple, isn't it? But now you have the right to ask, how does the helicopter move forward? After all, it doesn’t have any horizontal propeller, like, for example, a propeller-driven airplane. jet engine Same. What creates his craving?
As always, everything is elementary :-). This role is performed by the same main rotor. If the plane of rotation of the propeller is tilted, then the total aerodynamic force will tilt along with it. And now it can be divided into two components: a vertical one, which lifts the helicopter up and keeps it in the air, and a horizontal one, which makes it move forward. Although it would be more correct to say not forward, but towards where it is directed. You can do it sideways or backwards, which is what the helicopter does successfully, by the way.
That's all, actually. We answered the question about that. Of course, the theory and practice of this issue is much more complicated, but general principle flight is exactly like that.
I will say that in fact the main rotor, together with the massive axis and heavy accompanying mechanisms, does not deviate anywhere. This, to put it mildly, is difficult to implement and technically impractical. And yet the plane of rotation of the propeller tilts. In helicopter parlance, a “propeller misalignment” is created. It is achieved by changing the position of the blades, which are suspended from the axis on special hinges, and controls this process special device, called "". That's it, the helicopter flew... And exactly where we need it.
KA-52 Alligator. There is no tail rotor.
We will touch on all these abstruse concepts in a very popular (and non-abstruse :-)) manner in our further conversations, and now I will finally mention one necessary thing. You've probably all seen a small tail rotor on helicopters and asked yourself the question: “What is it for?” I answer. I think everyone, even ardent non-physics enthusiasts, have heard about Newton’s three laws. And if you haven’t heard, then take my word for it, I know what I’m saying :-). So the third law in popular form says: “Every action has an equal reaction.” It is according to this expression that the so-called reactive moment arises. That is, if the main rotor of a helicopter rotates, for example, to the right, this moment will tend to turn the helicopter body to the left (or vice versa). To eliminate this completely unnecessary tendency, there is a tail rotor. It works like a regular pulling one and, by creating thrust opposite to the reactive torque, it simply balances it. And if the helicopter needs to turn, then the thrust of this rotor changes due to the rotation of its blades.
There are plenty of helicopters without a tail rotor. These are, for example, the well-known KA-50 and KA-52. But they have, as it were, two main rotors on the same axis. And they rotate in different sides, thereby balancing the harmful reactive moment.
All. More than enough has been said already. Now if you are asked, you can easily answer this question. And I advise you to take a closer look at modern types this aircraft. They have now developed into a certain type that, in a certain sense, stands apart from traditional aviation and sometimes simply fascinates with its appearance and its capabilities... Although, however, to be continued...
P.S.
Finally, a small video featuring MI-24. Not Russian, unfortunately. This is how people care about technology, especially such a well-deserved one. The second video is Mi-24 aerobatics.
Photos and pictures are clickable.
a lifting force would have to arise that would exceed the weight of the aircraft, the legendary inventor believed. But we had to wait several centuries before this principle was realized.
Experimenters carried out experiments with flat wings quite successfully. By placing such a plate at a slight angle to the air flow, it was possible to observe how the lifting force arises. But a drag force also appears, which tends to blow the flat wing back. The researchers called the angle at which the air flow acts on the plane of the wing the angle of attack. The larger it is, the greater the lift and drag forces take on.
In the early days of aviation, researchers discovered that the most efficient angle of attack for a flat-shaped wing was 2-9 degrees. With a lower value it will not be possible to create the necessary lift force. And if the angle of attack is excessively large, unnecessary resistance to movement will arise - the wing will simply turn into a sail. Scientists call the ratio of lift to drag force the aerodynamic quality of the wing.
Modern airplanes have a significant weight. But the lifting force that arises at the moment of takeoff allows the heavy structure to break away from the surface of the earth. The secret lies in the correctly selected wing profile, in the accurate calculation of their area and angle of attack. If an airplane wing were completely flat, it would be impossible to fly a heavier-than-air craft.
Lift is used not only when taking off and keeping an airplane in the air. It is also needed to control the aircraft in flight. To do this, the wings are divided into a number of moving elements. When performing maneuvers, such flaps change their position relative to the fixed part of the wing. The aircraft has a horizontal tail, which serves as an elevator, and a vertical tail, which serves as a rudder. Such structural elements guarantee the aircraft stability in the air.
In order for an airplane or glider to fly, lift is needed, and this force is created by the wing. Therefore, the main thing in an airplane is the wing, because ultimately the entire airplane can be reduced to a flying wing, without a fuselage, without tail surfaces.
In a helicopter, the main rotor plays the role of a wing. Even if in aircraft There is nothing else except the main rotor; we can fundamentally call it a “helicopter”.
Probably, many in childhood made themselves such a “helicopter”, consisting only of one propeller cut from a piece of tin. The starting device for it was an ordinary spool of thread rotating on a rod.
However, the role of a helicopter's main rotor is much more multifaceted than that of an airplane wing.
The purpose of the main rotor is not yet limited to creating lifting force.
When you look at a helicopter in level flight, you will inevitably notice that the nose of the fuselage is tilted towards the horizon. In this case, the main rotor also turns forward.
The total aerodynamic force R, developed by the main rotor and directed perpendicular to the plane of rotation of the ends of the blades, in this case can be decomposed into two components: a vertically directed lift force, which supports the helicopter at a given height, and a force directed tangentially to the flight path, P , which on a helicopter is the thrust force. Due to this force, the helicopter flies forward. Thus, the main rotor in forward flight is also a pulling rotor.
However, the role of the main rotor is not limited to this. A helicopter, unlike an airplane, does not have control surfaces, such as ailerons, trim tabs, rudders and elevators. Yes, they would not make sense, since during the flight they would not be blown by the air flow and, therefore, could not serve control purposes.
After all, we know that in order to change the position of the body, an external force must be applied to it. During flight, the helicopter is surrounded by air, so external force can only be the result of interaction of any parts of the helicopter with the air environment. In order for air resistance to occur, the body must move at a higher speed. When a helicopter hangs in the air, not a single part of it meets this condition except the propeller. Therefore, the role of the helicopter control is also assigned to the main rotor. By operating the control stick, the pilot, with the help of special devices, which will be discussed in the following chapters, achieves a position that is equivalent to changing the plane of rotation of the main rotor. At the same time, the total aerodynamic force changes its direction propeller and both of its components. And if the lifting force is always directed vertically upward, then the second component is tangential to the flight path.
Depending on the angle of inclination of the total aerodynamic force, not only the direction, but also the magnitude of its components changes. Consequently, by controlling the main rotor, the pilot can change not only the flight direction, but also the flight speed.
To raise or lower the helicopter, the pilot also acts on the main rotor blades, reducing or increasing simultaneously and by the same amount the angle of installation of all blades.
If the engine fails on a helicopter, then by reducing the angles of attack of the blades, the pilot places the main rotor in the self-rotation position (autorotation). Supported by the lift generated by the propeller in this operating mode, the helicopter makes a safe gliding descent.
From the above, it is clear that to understand the structure and flight of a helicopter, one must first understand the operation of the main rotor; In order for a helicopter to fly successfully, the designer must ensure the reliability, first of all, of the main rotor.
Pilots, engineers, technicians and mechanics who fly and maintain helicopters must first and foremost ensure that the main rotor is in impeccable condition.
So, the main rotor is the main thing in a helicopter
There are extremely many modes of operation of a helicopter's main rotor. Each helicopter flight mode has its own main rotor operating mode. The main ones for a helicopter are: propeller mode, oblique blowing mode, self-rotation mode (augorotation) and vortex-solid mode.
Propeller mode occurs when a helicopter is ascending or hovering vertically.
The oblique blowing mode occurs during forward flight of a helicopter.
The self-rotation mode occurs when the helicopter engine is disconnected from the main rotor in flight, while the rotor rotates under the influence of air flow.
The vortex ring mode occurs when the helicopter descends. In this mode, the air flow, passing through the surface swept by the propeller from top to bottom, again approaches the propeller from above.
However, in some special cases, for example, in propeller mode, its operation is similar to the operation of an aircraft propeller. When the plane is on the ground or flying horizontally, its propeller is blown from the side of the plane of rotation (along the axis). When a helicopter is on the ground, hanging in the air or rising vertically, its main rotor is also blown from the side of the plane of rotation (along the axis). The only difference is that in an airplane the air jets pass through the plane of rotation of the propeller in the horizontal direction, from front to back, while in a helicopter they pass in the vertical direction, from top to bottom. In this case, the main rotor captures air from zone A from above and throws it, twisting, down into the zone. Air particles taken from zone A are replaced by air particles from environment and partially from zone B, but outside the plane of rotation of the propeller.
Before the main rotor was set into rotation, the air above and below the rotor was at rest. When the rotor begins to rotate, instruments brought into the area of action of the rotor, but located far from it, will show the observer that in the 0-0 section the air is -still in a state of relative rest. Its pressure is equal to atmospheric pressure, and its speed. The distance from the 0-0 section, where the influence of the screw is not yet observed, to the plane of rotation of the screw is a variable value, which depends on the viscosity of the medium and the accuracy of the instruments we use. The more accurate the device, the farther from the propeller it will register the presence of air speed, the particles of which will be directed towards the propeller.
If the air were deprived of viscous forces, then the action of the screw would have an effect infinitely far.
In fact, due to the fact that air is a viscous medium, the influence of the propeller ceases to be felt already at a distance of tens of meters.
Moving our instruments from the 0-0 section closer and closer to the section, we will notice a gradual increase in the speed of the air sucked in by the propeller. The speed that the air has when approaching the cross section is called the inductive suction speed. Based on the law of conservation of energy, kinetic energy (the energy of motion speed) cannot increase without some other type of energy decreasing. And indeed, along with the increase in air speed to w, we notice that the air pressure p0 decreases. This means that the increase in air speed occurred due to a decrease in pressure. Behind the propeller, the flow cross-section is compressed and an even greater increase in air speed occurs. It would seem that a further drop in pressure should have followed. However, immediately behind the propeller the pressure rises to p-2. Doesn't this contradict the law of conservation of energy? Yes, it contradicts, if we do not take into account the fact that the air from the outside (from the propeller) received additional energy (mechanical). Mechanical energy The propeller is converted into kinetic and potential energy of the flow, increasing both the speed and air pressure at the same time.
In the section immediately behind the propeller, the device shows us that the air, compared to the cross section, has a speed u, called the ejection speed. Moreover, the speed of ejection turns out to be twice the speed of suction.
Far behind the propeller, in the section (theoretically at an infinite distance), the air speed and pressure are restored to their original values. In this case, the flow energy is dissipated in space due to the presence of viscous forces.
This is the action of the propeller on the air, which is a consequence of the application of rotational energy to the propeller. This action corresponds to the response of air on the propeller, which manifests itself in the form of thrust force, which is the projection of the total aerodynamic force R onto the axis passing through the propeller hub perpendicular to the plane of its rotation. If the dynamometer connected to the propeller showed a zero thrust value when the propeller was stopped, then as the speed increases, the thrust will increase more and more. In hover and vertical climb modes in all other flight modes
The amount of thrust created by the propeller can not only be measured, but also calculated.
The control stick determines the cyclic pitch of the main rotor. With its help, the pilot controls the helicopter in roll and pitch. Working with the control stick while hanging is like balancing on the point of a needle. Almost every action requires corresponding correction by other controls. For example, to increase speed, the pilot pushes the stick away from himself, tilting the car forward. In this case, the vertical component in the propeller thrust vector decreases, and it is necessary to increase the overall pitch (raise the “step-throttle” lever) in order not to lose altitude.
1. Control knob. 2. Step-throttle lever. 3.Pedals. 4. Communication management. 5.Compass.
Step-throttle. By raising the pitch-throttle lever, the pilot increases the overall pitch (angle of attack of the blades) of the main rotor, thereby increasing thrust. In the event of a sharp increase in pitch, the reactive torque of the propeller changes, and the helicopter tends to change course. To stay on the chosen trajectory, the pilot works synchronously with the step-throttle lever and the pedals.
The pedals determine the pitch of the stabilizing (“tail”) rotor. With their help, the pilot controls the course of the car. Sharp work pedals affects the reactive moment of the stabilizing propeller and, despite its insignificant mass, has some effect on pitch. “Experienced trainers sometimes show cadets a trick by fixing the control stick and the “step-throttle” and controlling the altitude and speed of the flight, only slightly waving the tail,” says Sergei Druy, “this is how rumors about “radio-controlled helicopters” and other magic appear.”
6. Variometer (vertical speed indicator). 7. Attitude horizon. 8. Airspeed indicator. 9. Tachometer (on the left is the engine speed indicator, on the right is the propeller). 10.Altimeter. 11. Pressure indicator in the intake manifold (gives an idea of the engine power reserve at a given load and weather conditions). 12. Signal lamps. 13. Air temperature in the intake tract. 14.Clock. 15. Engine instruments (oil pressure and temperature, fuel level, on-board voltage). 16. Lighting control. 17. Clutch power drive switch (transmits torque to the propeller after the engine warms up). 18. Main switch. 19. Ignition switch. 20. Cabin heating. 21. Cabin ventilation. 22. Intercom mixer. 23.Radio station.
Distribution of attention
The most important skill to fly a helicopter is right choice viewing directions. Cadets are taught to take off and land while looking at the ground at a distance of 5-15 m in front of them. This simple geometry. If you look further, right down to the horizon, you may not notice significant changes in height. Helicopter pilots look directly “under the edge of the cockpit” and notice millimeter-scale changes in height. If the cadet chooses the same direction of gaze, he will see small fluctuations, but will not be able to correct them - he will not have enough skills and fine motor skills that come with experience. Therefore, when training, the trainer suggests that the cadet start by looking at 15 m, and then gradually reduce this distance.
The “valve” on the central tunnel controls the friction of the control handle. With its help, the pilot can increase the resistance on the handle until it is completely locked. This feature helps on long cross-country flights.
The basic direction of view in flight along the route is “hood-horizon”. If the position of the horizon relative to the hood does not change, it means that the helicopter is flying at a given altitude at a constant speed. A “peck” will most likely mean an increase in speed and a loss of altitude; a tilt of the horizon line will mean a change in course. "IN good weather“You can fly with the instrument panel taped up,” says Sergei Drui, “but you won’t fly far with the cockpit windows taped up.”
Step or gas?
Most modern helicopters have automation that regulates the fuel supply to the engine to keep the rotor speed within a narrow operating range. By turning the handle of the “step-throttle” lever, the pilot can independently control the fuel supply. During flight, the pilot can feel how the handle itself turns slightly in his hand - this is an automatic operation. It happens that newcomers in tension squeeze the handle, preventing the machine from working, and the sound signal, warning of a drop in speed.
Autorotation
The autorotation mode, in which the propeller with a small angle of attack rotates using the energy of the incoming air flow, allows you, if necessary, to select a landing site and land with the engine turned off. To maintain the mode, the pilot looks at the tachometer. If the propeller speed drops below the operating range, you need to smoothly reduce the overall pitch of the propeller. If the speed increases, the collective pitch needs to be increased. At the same time, the helicopter remains fully controllable in terms of heading, roll and pitch.
The maximum flight altitude is determined by two “ceilings”: static and dynamic. In the first case we're talking about about vertical lifting only with the help of a rotor. This figure is usually lower. In the second case, lifting is carried out both with the help of a screw and due to the speed of linear movement. In this case, you can go higher.
Helicopter: features
In an aircraft, it is formed due to the speed and configuration of the wing. A helicopter rises in a completely different way. The maximum flight altitude rarely exceeds 3000-3500 m. A power plant and a main rotor are used for lifting. The speed is not comparable to airplanes, but a helicopter can easily take off without a run-up and land on an unprepared runway, hover in place, move sideways.
According to the instructions, pilots are prohibited from turning off their engines while landing at altitudes above 3000 meters. Normal operation for most helicopters, up to 4.5 km is possible in normal mode. Above this threshold, the air becomes rarefied and the propeller blades must be given maximum angles of attack. And this can lead to emergency situations.
Varieties
To objectively determine the indicators, it is necessary to identify what type of helicopter it is. The maximum flight altitude can be set for four subclasses of rotorcraft, into which they are divided by the Fédération Aéronautique Internationale (FAI) in accordance with their design features.
In addition to helicopters, gyroplanes are also defined, in which the main rotor does not change the angle of inclination and is used only to create lift. Another subclass is tiltrotors. Their propellers, together with their engines, are directed upward during takeoff, and during horizontal flight they turn and operate like aircraft. A separate subclass of rotorcraft is distinguished, in which, in addition to the main rotor, lateral aerodynamic planes on the body (wings) are used to create lift.
All helicopters are also divided into five groups depending on take-off weight: from 500 kg to 4500 kg. In addition, the type of appointment is determined: civilian or military. Among them, separate subclasses can be distinguished depending on the specifics of use: transport, multi-purpose, search and rescue, fire, agricultural, crane helicopters and others.
Helicopter: maximum flight altitude
Both static and dynamic “ceilings” have limits. Restrictions are introduced to determine the limits, exceeding which can lead to disruption of the air flow from the rotor blades. Rotorcraft remain more confident in the air at altitudes of up to 4500 m, with a maximum “ceiling” of up to 6 km for individual aircraft.
The maximum flight altitude of the helicopter, recorded as an absolute record, is 12442 m. It was set by the French aeronaut Jean Boulet. His Aerospatiale "Lama", belonging to the "helicopters" subclass, was able to overcome the 12-kilometer mark in 1972. That flight could have ended fatally, since at an altitude where the temperature was below - 60 ° C, the engine stalled. The pilot had to set another record - the maximum altitude descent in the self-rotating mode of the main rotor.
Helicopter "Shark"
The twin-rotor vehicle with a coaxial arrangement adopted for service - the Ka-50 - has a static ceiling, defined technical characteristics at the level of 4000 meters. The maximum dynamic flight altitude of the Akula helicopter can be up to 5500 meters. Flight speed in cruising mode is 260 km/h, sideways - 80 km/h, backwards - up to 90 km/h. It gains altitude at 28 m/s. Capable of performing a complete “dead loop”, although such a maneuver is dangerous due to the high probability of the screws getting stuck.
For comparison maximum height The flight range of the Mi-26 helicopter is 6500 m, and that of the Mi-28 is 5800 m. The American Apache AN-64 can rise to 6400 m. The modernized Ka-52 Alligator, like the Shark, flies at an altitude of 5700 m.
